During the next year studies will continue on methods for incorporation of fluorine-18 into various positions on steroid molecules. In this manner, we shall produce derivatives which will allow us to investigate and utilize the differences in metabolism and distribution between various species. The effect of specific activity on the distribution of steroids will be investigated in rats. Species differences in the metabolism and distribution of fluorinated steroids will be investigated to provide the understanding necessary to design molecules for imaging the adrenal glands.